1. Field of Invention
The invention relates to prostaglandin derivatives. More particularly, this invention relates to 9,15-dioxygenated derivatives of prost-13-enoic, prosta-4,13-dienoic and prosta-5,13-dienoic acids having lower alkyl substituents, to homologs thereof, to intermediates used in their preparation and to a process for preparing these compounds.
2. Description of the Prior Art
A prostaglandin (PG) is a naturally occurring C-20 fatty acid. The natural prostaglandin molecule contains a cyclopentane nucleus with two side chains in trans configuration. The fundamental structure is called prostanoic acid and is conventionally represented as follows: ##STR1##
The chemistry and pharmacological effects of the prostaglandins have been the subject of several recent reviews; for example, see E. W. Horton, Physiol. Rev., 49, 122 (1969), J. F. Bagli in "Annual Reports in Medicinal Chemistry, 1969", C. K. Cain, Ed., Academic Press, New York and London, 1970, p. 170, and J. E. Pike in "Progress in the Chemistry of Organic Natural Products", Vol. 28, W. Herz, et al. Eds., Springer Verlag, New York, 1970, p. 313.
The pharmacological effects known to be associated with the prostaglandins relate to the reproductive, cardiovascular, respiratory, gastrointestinal and renal systems.
Due to the increasing interest in these natural products a rather extensive effort has been given recently to the synthesis of prostaglandins and their analogs. Included among these syntheses are several synthetic methods for the preparation of 9,15-dioxygenated derivatives of prostanoic or prost-13-enoic acid. For example, the synthesis of the first pharmacologically active 9,15-dioxygenated prostanoic acid derivative, 9.beta.,15.xi.-dihydroxyprost-13-enoic acid (11-desoxyprostaglandin F.sub.1) was reported in detail by J. F. Bagli, T. Bogri and R. Deghenghi, Tetrahedron Letters, 465 (1966). A significant simplification and modification of that process was described by Bagli and Bogri in U.S. Pat. No. 3,455,992, issued July 15, 1969, whereby 9.beta.,15.xi.-dihydroxyprost-13-enoic acid as well as homologs thereof were obtained, see also Bagli and Bogri, Tetrahedron Letters, 5 (1967).
Further improvements in the synthesis of 9,15-dioxygenated derivatives of prostanoic acid have been described by Bagli and Bogri in Tetrahedron Letters, 1639 (1969) and German Offenlegungsschrift No. 1,953,232, published Apr. 30, 1970, and in British patent specification No. 1,097,533, published Jan. 3, 1968.
Other recent syntheses of 9,15-dioxygenated derivatives are reported in Belgian Pat. No. 766,521, published Nov. 3, 1971, P. Crabbe and A. Guzman; Tetrahedron Letters, 115 (1972), M. P. L. Caton, et al., Tetrahedron Letters, 773 (1972), C. J. Sih, et al., Tetrahedron Letters, 2435 (1972), F. S. Alverez, et al., J. Amer. Chem. Soc., 94, 7823 (1972), A. F. Kluge, et al., J. Amer. Chem. Soc., 94, 9256 (1972), and N. A. Abraham, Tetrahedron Letters, 451, 1973.
More recently, Bagli and Bogri have extended the scope of their processes for preparing 9,15-dioxygenated derivatives of prostanoic acid to include the preparation of 9-oxo-15-hydroxy prostanoic acid derivatives having an alkyl substituent at position 15, U.S. Pat. No. 3,671,570, issued June 20, 1972. These 15-alkyl derivatives possess hypotensive, antihypertensive, bronchospasmolytic and gastric acid secretion inhibiting properties, as well as inhibiting the aggregation of platelets and promoting the disaggregation of aggregated platelets.
It is noteworthy that the synthetic 9,15-dioxygenated prostanoic acid derivatives described above possess a number of the biological activities of the natural compounds although they lack the 11-hydroxyl of the latter.
In the natural series attention has been focused recently on certain 15-methyl and 16,16-dimethyl derivatives.
15-Methyl PGF.sub.2.alpha. and 15-methyl PGE.sub.2 methyl esters have been reported to interrupt pregnancy in the rhesus monkey and in the human, K. T. Kirton et al., Ann. N.Y. Acad. Sci., 180, 455 (1971). Furthermore, 15(R)-methyl and 15(S)-methyl PGE.sub.2 has been reported to inhibit gastric secretion, see Medical World News, Oct. 20, 1972, p. 70M. Likewise, 16,16-dimethyl PGE.sub.2 methyl ester has been described as effective in inhibiting gastric acid secretion, Chemistry and Engineering News, Oct. 16, 1972, p. 12.
It is worth noting at this point that the natural PGE.sub.1, PGE.sub.2, PGF.sub.1.alpha. and PGF.sub.2.alpha. do have the disadvantage of being relatively unstable, see T. O. Oesterling, et al., J. Pharm. Sci., 61, 1861 (1972). For example, it is well known that the 11-hydroxy group of PGE.sub.1 and PGE.sub.2 participates readily in dehydration reactions under both basic and acidic conditions, see S. Bergstrom et al., J. Biol. Chem. 238, 3555 (1963), E. J. Corey et al., J. Amer. Chem. Soc., 90, 3245 (1968), J. E. Pike et al., J. Org. Chem. 34, 3552 (1969) and "The Prostaglandins, Progress in Research", S. M. M. Karim, Ed., Wiley-Interscience, New York, 1972, p. 10.
As realized by those skilled in the art this inherent disadvantage of the natural compounds must always be taken into account when considering the practical aspects of preparation, formulation of storage of these compounds. In contrast, the compounds of the present invention are free from this disadvantage.
In brief, although 15-alkylated derivatives of both the 9,15-dioxygenated derivatives of prostanoic acids, i.e. 11-deoxyprostaglandins, and the 15- and 16-alkylated derivatives of natural prostaglandins have been described as exhibiting effects on the gastrointestinal system, and although certain methyl esters of the 15-alkylated natural derivatives have been described as having effects on the reproductive system, it would appear that the latter effects have never been associated with 15- and/or 16-alkyl analogs of the 9,15-dioxygenated derivatives.
It is the purpose of the present application to disclose the discovery of certain stable 15-alkylated and/or 16-alkylated derivatives of the 9,15-dioxygenated derivatives of prostanoic acid having unexpected high activity regarding effects on the reproductive system. More specifically, the compounds of this invention are effective agents for inducing abortion and for synchronization of estrus and regulation of ovulation in animals.